We plan to study further the physiological relevance of parathyroid hormone (PTH) metabolism by investigating various physiochemical conditions which alter peripheral breakdown of the secreted hormone. We plan to investigate factors, other than divalent cations (intestinal hormones) which may affect PTH secretion. These studies will be done utilizing the dog model we have recently perfected for measuring PTH secretion directly in vivo. Our current major research goal direction is to define the interrelationships which may exist between vitamin D and PTH--- how these two hormones affect each other's secretion and metabolism. BIBLIOGRAPHIC REFERENCES: Reiss, E. and Canterbury, J.M. The effects of phosphate on parathyroid hormone secretion. In: Talmage, R.V., Owen, M. and Parsons, J.A. (Eds.) Calcium Regulating Hormones, Proceedings of the Fifth Parathyroid Conference, Oxford. pp. 66-71. Excerpta Medica, Amsterdam. 1975. Reiss, E. and Canterbury, J.M. Radioimmunoassay and its application to the diagnosis of hyperparathyroidism. In: Kryston, L.J. and Shaw, R.A. (Eds.) Endocrinology and Diabetes. pp. 173-187. Grune and Stratton, New York, 1975.